It is a one-mana legendary monkey pirate creature at 2/2 that, when it deals combat damage to an opposing player, creates a treasure token and exiles the top card of the defending player's library, and you can cast that card until the end of the turn
The best choice often lies in opposing commanders: Everybody wants to cast them frequently, so finding a common number does a lot
Thats also why the card disadvantage of playing Mox Diamond, Chrome Mox or Lions Eye Diamond matters far less, as games are faster and end much more abruptly
The conditions are that you need a chunky creature and that youre hitting a smaller one, but thats not hard for Gruul particularly with so many cheap and pivotal creatures being deployed to curve out
While it looks tough to access at first, the card essentially gives you two land drops itself, one on entry and one when your Earthbent land is inevitably removed somehow, so it shouldnt be hard to get going
West End Games had Star Wars